Selected Quarterly Financial Data (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Selected Quarterly Financial Information [Abstract]
Total revenues	$ 18,984.3	$ 18,557.0	$ 18,473.4	$ 17,859.4	$ 17,901.7	$ 17,855.5	$ 17,690.3	$ 17,576.0	$ 73,874.1	$ 71,023.5	$ 61,497.2
Income (loss) from continuing operations before income taxes	887.1	1,087.2	1,263.7	1,130.1	469.9	879.7	1,208.1	1,282.5	4,368.1	3,840.2	3,858.3
Income from continuing operations	506.7	630.9	731.1	691.4	308.9	653.8	799.3	872.3	2,560.1	2,634.3	2,651.0
Income (loss) from discontinued operations, net of tax	0	0	0	9.6	(160.7)	2.4	0.8	12.9	9.6	(144.6)	4.5
Net income	$ 506.7	$ 630.9	$ 731.1	$ 701.0	$ 148.2	$ 656.2	$ 800.1	$ 885.2	$ 2,569.7	$ 2,489.7	$ 2,655.5
Basic net income per share - continuing operations	$ 1.88	$ 2.31	$ 2.64	$ 2.43	$ 1.05	$ 2.20	$ 2.67	$ 2.88	$ 9.28	$ 8.83	$ 8.25
Basic net income (loss) per share - discontinued operations	$ 0.00	$ 0.00	$ 0.00	$ 0.03	$ (0.55)	$ 0.01	$ 0.00	$ 0.04	$ 0.03	$ (0.49)	$ 0.01
Basic net income per share	$ 1.88	$ 2.31	$ 2.64	$ 2.46	$ 0.50	$ 2.21	$ 2.67	$ 2.92	$ 9.31	$ 8.34	$ 8.26
Diluted net income per share - continuing operations	$ 1.80	$ 2.22	$ 2.56	$ 2.37	$ 1.02	$ 2.15	$ 2.64	$ 2.85	$ 8.96	$ 8.67	$ 8.17
Diluted net income (loss) per share - discontinued operations	$ 0.00	$ 0.00	$ 0.00	$ 0.03	$ (0.53)	$ 0.01	$ 0.00	$ 0.04	$ 0.03	$ (0.47)	$ 0.01
Diluted net income per share	$ 1.80	$ 2.22	$ 2.56	$ 2.40	$ 0.49	$ 2.16	$ 2.64	$ 2.89	$ 8.99	$ 8.20	$ 8.18